The primary goal during the next year is to complete the atomic model of the pea lectin dimer with an improved 3 Angstrom electron density map incorporating phases based on a partial model of high quality that includes over 70% of the nonhydrogen atoms in the dimer. The final model will be constructed with the aid of an Evans & Sutherland Multi-Picture System and model-fitting software, primarily the program FRODO. A report describing the model will be prepared at this stage. It is expected that examination of this pea lectin model and its comparison to that of Concanavalin A will answer most of the fundamental questions concerning similarities and differences between the structures of these lectins and concerning relationships between their sequence and structural similarities. A second goal is to begin extension of this study to higher resolution with the data collected at the Synchrotron Radiation Source at Daresbury, England. Full analysis of the data remains to be completed and a strategy to best utilize the data must be devised. At present, the next step in resolution is expected to be 2.2 Angstrom. Most of the methods used to prepare the 3 Angstrom map are applicable to an extension to 2.2 Angstrom, and requirements for extraordinary new procedures are not anticipated. A third goal is to take the first steps in preparation for extension of this study to the limit of resolution, 1.2 Angstrom. Data collection for this extension, as presently planned, will take advantage of lower wavelength and electronic detection capabilities recently developed at the Daresbury laboratory. This data collection will also be made at low temperature, -10 C, to minimize crystal decay over long exposure times with the expectation that only one or two crystals might be required. Initial experiments with crystals at low temperature and with development of a mother liquor suitable at low temperature must be extended.